Iterative regularization algorithms for constrained image deblurring on graphics processors

The ability of the modern graphics processors to operate on large matrices in parallel can be exploited for solving constrained image deblurring problems in a short time. In particular, in this paper we propose the parallel implementation of two iterative regularization methods: the well known expectation maximization algorithm and a recent scaled gradient projection method. The main differences between the considered approaches and their impact on the parallel implementations are discussed. The effectiveness of the parallel schemes and the speedups over standard CPU implementations are evaluated on test problems arising from astronomical images.     

Notes on a paper of Mess

These notes are a companion to the preceding paper by Geoffrey Mess, “Lorentz spacetimes of constant curvature”. Mess’ paper was written nearly 20 years ago and so we hope these notes will be useful as a guide to the literature that has appeared in the intervening years. Lars Andersson was supported in part by the NSF, contract no. DMS 0407732 and Thierry Barbot was supported by CNRS, ACI “Structures géométriques et Trous Noirs”.     

Principal parts bundles on projective spaces and quiver representations

We study the principal parts bundles \(\mathcal {P}^{k}\mathcal {O}_{\mathbb {P}^{n}}(d)\) as homogeneous bundles and we describe their associated quiver representations. With this technique we show that if n≥2 and 0≤d<k then there exists an invariant decomposition \(\mathcal {P}^{k}\mathcal {O}_{\mathbb {P}^{n}}(d)=Q_{k,d}\oplus(S^{d}V\otimes \mathcal {O}_{\mathbb {P}^{n}})\) with Q _k,d a stable homogeneous vector bundle. The decomposition properties of such bundles were previously known only for n=1 or k≤d or d<0. Moreover we show that the Taylor truncation maps \(H^{0}\mathcal {P}^{k}\mathcal {O}_{\mathbb {P}^{n}}(d)\to H^{0}\mathcal {P}^{h}\mathcal {O}_{\mathbb {P}^{n}}(d)\), defined for any h≤k and any d, have maximal rank.     

Acid mediated tunability of stimulated laser emission from dye doped chiral microdroplets

Abstract

In the last decade, the possibility to use liquid crystal droplets as optical micro-cavities and lasers has attracted much attention since it paves the way for many applications in the field of sensors or tunable photonics. Several techniques can be used to obtain small micro-resonators as, for example, dispersing a cholesteric liquid crystal inside an immiscible isotropic fluid to create an emulsion. Since liquid crystals are extremely sensitive to external factors as temperature or external fields, laser tuning can be easily achieved. Here, we report on the possibility to tune the laser emission from dye doped cholesteric liquid crystals microdroplets dispersed in a glycerol matrix in presence of nitric acid molecules in the emulsion. Using a fluorescent dye with pH dependent optical properties, the emitted laser wavelength can be tuned in a range of 60?nm. This effect could find applications for the development of spectroscopy based sensors.     

Polymerization of 1,3‐cyclohexadiene with nickel/MAO catalytic systems

The polymerization of 1,3‐cyclohexadiene with nickel bis(acetylacetonate) activated by methylaluminoxane affords poly(1,3‐cyclohexadiene) in high yields; the same catalyst is unable to polymerize larger conjugated cyclic diolefins or copolymerize 1,3‐cyclohexadiene with styrene. In the latter case, the homopolymer of the diolefin is obtained. The catalyst activity increases with increasing reaction temperature, nickel concentration, and aluminum/nickel ratio or with the addition of triisobutylaluminum to the reaction medium. The obtained poly(1,3‐cyclohexadiene) samples are high‐melting crystalline polymers (melting temperature ∼ 320 °C) that are insoluble in all common organic solvents. With bis(cyclopentadienyl)nickel in place of nickel bis(acetylacetonate), the activity is much lower, but the polymer is more stereoregular, as indicated by the slightly higher value of the melting temperature. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3004–3009, 2000     

Polymerization of styrene with nickel complex/methylaluminoxane catalytic systems

Polymerization of styrene using catalytic systems based on nickel derivatives and methylaluminoxane (MAO) was studied. Among tested catalysts, nickel bis(acetylacetonate) and nickel dichloride show the maximum activity. Bis(phosphine)nickel dichlorides exhibit lower activity, depending on the nature of the phosphine ligand. Polymer yields decrease by lowering the catalyst concentration, by increasing the reaction temperature, or by carrying out the polymerization in a polar donor solvent. Weight average molecular weight of most of the prepared polystyrenes ranges from 9000 to 25,000, with polydispersity indexes of 1.6–3.8. However, polystyrene prepared in dioxane solvent exhibits a small fraction of very high molecular weight (about 140,000). From NMR analysis, the products seem generally to be constituted of two polymers with different steric microstructure: atactic polystyrene and partially isotactic polystyrene (ca. 75–85% meso diads). Catalytic site specificity is correlated with the type of nickel ligand, while the effect of reaction temperature is less defined. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 2119–2126, 1998     

The “Historical Materials BAG”: A New Facilitated Access to Synchrotron X-ray Diffraction Analyses for Cultural Heritage Materials at the European Synchrotron Radiation Facility

The European Synchrotron Radiation Facility (ESRF) has recently commissioned the new Extremely Brilliant Source (EBS). The gain in brightness as well as the continuous development of beamline instruments boosts the beamline performances, in particular in terms of accelerated data acquisition. This has motivated the development of new access modes as an alternative to standard proposals for access to beamtime, in particular via the “block allocation group” (BAG) mode. Here, we present the recently implemented “historical materials BAG”: a community proposal giving to 10 European institutes the opportunity for guaranteed beamtime at two X-ray powder diffraction (XRPD) beamlines—ID13, for 2D high lateral resolution XRPD mapping, and ID22 for high angular resolution XRPD bulk analyses—with a particular focus on applications to cultural heritage. The capabilities offered by these instruments, the specific hardware and software developments to facilitate and speed-up data acquisition and data processing are detailed, and the first results from this new access are illustrated with recent applications to pigments, paintings, ceramics and wood.     

New Pharmacological Strategies against Pancreatic Adenocarcinoma: The Multifunctional Thiosemicarbazone FA4

A new sigma-2 (σ2) receptor ligand (FA4) was efficiently synthesized and evaluated for cytotoxic, proapoptotic, and antimigratory activity on pancreatic ductal adenocarcinoma (PDAC) primary cell cultures, which restrained the aggressive and chemoresistant behavior of PDAC. This compound showed relevant antiproliferative activity with half maximal inhibitory concentration (IC50) values ranging from 0.701 to 0.825 μM. The cytotoxic activity was associated with induction of apoptosis, resulting in apoptotic indexes higher than those observed after exposure to a clinically relevant concentration of the gemcitabine, the first-line drug used against PDAC. Interestingly, FA4 was also able to significantly inhibit the migration rate of both PDAC-1 and PDAC-2 cells in the scratch wound-healing assay. In conclusion, our results support further studies to improve the library of thiosemicarbazones targeting the σ-2 receptor for a deeper understanding of the relationship between the biological activity of these compounds and the development of more efficient anticancer compounds against PDAC.     

Automated Phasor Segmentation of Fluorescence Lifetime Imaging Data for Discriminating Pigments and Binders Used in Artworks

The non-invasive analysis of fluorescence from binders and pigments employed in mixtures in artworks is a major challenge in cultural heritage science due to the broad overlapping emission of different fluorescent species causing difficulties in the data interpretation. To improve the specificity of fluorescence measurements, we went beyond steady-state fluorescence measurements by resolving the fluorescence decay dynamics of the emitting species through time-resolved fluorescence imaging (TRFI). In particular, we acquired the fluorescence decay features of different pigments and binders using a portable and compact fibre-based imaging setup. Fluorescence time-resolved data were analysed using the phasor method followed by a Gaussian mixture model (GMM) to automatically identify the populations of fluorescent species within the fluorescence decay maps. Our results demonstrate that this approach allows distinguishing different binders when mixed with the same pigment as well as discriminating different pigments dispersed in a common binder. The results obtained could establish a framework for the analysis of a broader range of pigments and binders to be then extended to several other materials used in art production. The obtained results, together with the compactness and portability of the instrument, pave the way for future in situ applications of the technology on paintings.